09/07/2026 8:38 am
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Automotive Q&A
Mercedes W205 NOx fault remains after sensor replacement
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A W205 diesel received the correct downstream NOx sensor for a heater fault. The heater code is gone, but a plausibility code remains and downstream values stay fixed until the key is cycled. Wiring voltage and ground are normal, and the old sensor control unit appears in the scan history.
Does this platform require commissioning or adaptation of the replacement sensor?
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10/07/2026 8:12 am
Check the VIN-specific replacement procedure. Many smart NOx sensors include a control unit whose software identity, variant coding or learned values must be recognized by the engine controller. Verify the new part number, network communication, heater release and sensor status before performing the stated teach-in.
Do not use adaptation to hide an installation or exhaust fault. Once communication and installation are confirmed, carry out the guided commissioning with stable battery support, then run the specified plausibility drive.
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11/07/2026 8:12 am
The sensor was physically correct but had not completed guided commissioning. After the supported teach-in, its status changed to active and the downstream value responded normally. The plausibility drive completed without another code.